The present invention relates to systems for positioning and manipulating loads, and more particularly, to systems for positioning and manipulating test heads.
Test heads are often utilized in the testing of integrated circuits. In order to use a test head to test integrated circuits, the test head is typically “docked” to a piece of peripheral equipment such as a prober or a device handler (hereinafter “peripheral”). A test head manipulator is typically used to position and manipulate the test head during the docking operation.
In docking a test head to a peripheral, it is desirable that the test head be moveable in a number of directions (i.e., that the test head have a number of degrees of freedom). Further, it is, also desirable to have the test head be compliantly moveable with respect to various degrees of freedom (i.e., the test head is substantially weightless or may be moved with a relatively small amount of externally applied force with respect to each of the degrees of freedom).
If a test head can move (in conjunction with the test head manipulator) along and rotate about each of X-axis, Y-axis, and Z-axis, the manipulator is said to provide at least six (6) degrees of freedom. If a test head can be moved compliantly, both linearly and rotationally, with respect to its own axes then the test head is said to be compliant with six (6) degrees of freedom.
Because test heads are typically very expensive, it is often desirable to use the same test head to dock with various different peripherals. For example, the same test head may be used to dock in a horizontal plane with a device handler (e.g., a test head may dock with a device handler from below the device handler) and a prober (e.g., a test head may dock with a prober from above the prober). In order to dock with various different types of peripherals, a test head manipulator desirably has a long vertical stroke (e.g., a long vertical range of motion). However, because of size constraints on test heads and the associated manipulators, this is not always practical. Additionally, certain test head manipulator systems utilize pneumatic cylinders to position and manipulate test heads in the vertical direction. In such a design, the vertical stroke provided by the test head manipulator is limited by the stroke of the pneumatic cylinder arrangement. Often, with larger test heads, the stroke of a pneumatic cylinder arrangement may be inadequate to provide a vertical range of motion adequate for docking a test head with the different types of peripherals.
As provided above, in systems for the docking of a test head, it is sometimes desirable to provide complaint motion in each of the test head's six (6) degrees of freedom. This means that during docking, a test head manipulator desirably balances the test head in a substantially weightless condition in each of the these six (6) degrees of freedom such that an operator can move the test head manually in each of the directions with relatively little force. However, as test heads have become larger and heavier, the physical force required to manually manipulate the test head in certain directions (even in a compliant state) may be difficult if not impossible for certain operators to provide.
As such, it would be desirable to provide a test head positioning and manipulation system addressing the above recited deficiencies.